Really concerned about AF ratio

[gusu]

So my AF ratio at 10 PSI is 15-16 my friend who has been working on a few SRT-4s that are all pretty good for being built by a self taught. Anyway he said that he was wondering why the car hasn't blown up by now.

Is this something I should really worry about? I've searched for a few days trying to find information I can understand with absolutely no luck at all.

I really hate to ask for information in a area that isn't specifically for that but I don't have enough posts and this could be potentially dangerous to myself and others, if he is correct.

 

[matthewdesigns]

Well, that could be any number of things, from gauges reading incorrectly to a clogged filter or injectors, to a failing pump, pre-wbo2 sensor exhaust leak, etc.

Please fill out your member profile so we have an idea of what modifications your car has, and that will be a start.

In the mean time, how old is the wbo2 sensor? Are you sure you are running only 10psi of boost, or is the gauge reading incorrectly due to a leak in the line? What turbo is it that you are using at 10psi? Pump and injector sizes? Do you have a logger, and if so, what's your injector duty cycle (IDC) and timing look like when it's this lean?

 

[gusu]

Well the only mods are a full 3 inch tubular exhaust and some gauges that is it really.

I have a Palm that was used for logging but I need to get new batteries for it.

 

[matthewdesigns]

Before you start having to buy parts or take apart too much stuff , here are a couple things to look into.

Are you going WOT when it reads 15-16:1 at 10psi, or is that at partial throttle? Are you only building 10psi of boost total at WOT, or is that where you are letting off due to the afr's? What rpm is that?

Do a boost leak test to see if you have a hole in the line to the boost gauge, verify that it's a hard plastic line (not softer rubber like vac lines), and that the hard line is not kinked anywhere. That will help rule out everything but the gauge itself.

Grab some batteries and see what your IDC's look like at WOT and at a cruise, and your fuel trims at a cruise. Also take a look at timing at WOT, b/c your timing ought to be taking a hit at that lean a condition due to knock. Start a log at 2500rpm in 3rd gear, put your foot on the floor, and don't let off until you are scared by the afr's . If you can make it to redline, great, but I wouldn't push it, personally. What fuel are you using btw?

Take a look under the car and see if the fuel lines have been kinked/dented in any way to restrict flow. If your wbo2 sensor is easy to get to, see if you can borrow a known good one and swap it in to see if that's the problem. IIRC the sensors start reading lean once they go bad.

 

[gusu]

Well last night I was messing around because my friend was like "Try redlining it". So I did and after that it has been reading high 13s and low 14s with the very occasional spike to 15. At this point I think it might be the gauge.

 

[matthewdesigns]

More likely the sensor than gauge, but they could both go bad I guess. Do check for exhaust leaks ahead of the sensor before you go dropping any coin on new wbo2 parts, because even small leaks can cause big changes in the reading.

 

[gusu]

Alright thanks for the info. I really appreciate it!

 

[tkelly27]

Fill out your profile. If you have a wb that can be calibrated, do so.